1. Field of the Invention
The present invention is in the field of industrial speed reduction drives and relates more particularly to a compact and cost efficient rotary speed reduction drive.
2. Prior Art
Conventional rotary speed reducers for industrial application include, in general, chain and sprocket drives, and belt and pulley or sheave drives. Both of the noted drive types have limited speed reduction capabilities when used with a single belt or chain flight.
Specifically, it is generally recognized that for significant transmission of torque a limitation of about 3:1 to 4:1 ratio is about the maximum which may be practicably employed. This limitation is engendered in part by the fact that in a sprocket only a limited number of teeth of the driving sprocket will engage the chain and, thus, there is a limit to the stress which may be applied to such small proportion of the sprocket teeth.
Similarly, there are limitations on the minimum radius of pulley to which a belt may be adapted since excessive flexing results in premature cracking and belt wear, thus mandating the use of relatively large drive pulleys and accordingly substantially larger output pulleys. In order to achieve, with a belt and pulley or chain and sprocket drive, speed reductions in excess of about 4:1 it is mandatory to use multiple sets of belts or chains, with resultant cost increases due to the necessity for providing additional shafts and bearings therefor. Moreover, the use of speed reducers which incorporate three or more shafts increases the bulk of the speed reducing unit.
Gear reduction drives suffer from the same disadvantage noted above and, in addition, are inherently more expensive than chain or belt drives due to the machining operation and metal treatment operation associated with gear manufacture plus the additional cost of lubricant encasing housings. The limitations of various reduction drives are well known in the industry and need not be further discussed.
It is known to provide, for specialized drive uses, planetary gear reduction units wherein a drive gear drives planetary gears which are meshed in addition with a stator gear to drive an output shaft connected to the planets. Such devices are extremely expensive due to the multiplicity of gears and bearings involved, the precision with which the same need be constructed, inherent high cost of gear fabrication, etc.